A virtual world (may also be referred to as virtual reality, virtual environment, or synthetic environment) is a computer-based simulated environment. Virtual reality is often used for various types of gaming as well as training purposes. For instance, a fully immersive virtual reality that uses a head-mounted display (HMD) allows a user to train through a wide variety of terrains, situations and scenarios. Virtual reality may also be used in flight simulations and various other training operations.